DeinoMPI

The Great and Terrible implementation of MPI-2

MPI_Request_get_status

Nondestructive test for the completion of a Request

int MPI_Request_get_status(
  MPI_Request request,
  int *flag,
  MPI_Status *status
);

Parameters

request: [in] request (handle)
flag: [out] true if operation has completed (logical)
status: [out] status object (Status). May be MPI_STATUS_IGNORE.

Remarks

This call is useful for accessing the information associated with a request, without freeing the request (in case the user is expected to access it later). It allows one to layer libraries more conveniently, since multiple layers of software may access the same completed request and extract from it the status information.

Sets flag=true if the operation is complete, and, if so, returns in status the request status. It sets flag=false if the operation is not complete.

Unlike MPI_Test, MPI_Request_get_status does not deallocate or deactivate the request. A call to one of the test/wait routines or MPI_Request_free should be made to release the request object.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as mallocor other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierris an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGERin Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS: No error; MPI routine completed successfully.

Example Code

The following sample code illustrates MPI_Request_get_status.

#include "mpi.h"
#include <stdio.h>

/* Test Request_get_status */

int main( int argc, char *argv[] )
{
    int errs = 0;
    int rank, size, source, dest;
    int buf[2], flag, count;
    MPI_Comm comm;
    MPI_Status status, status2;
    MPI_Request req;

    MPI_Init( &argc, &argv );

    comm = MPI_COMM_WORLD;
    /* Determine the sender and receiver */
    MPI_Comm_rank( comm, &rank );
    MPI_Comm_size( comm, &size );
    source = 0;
    dest = size - 1;

    if (rank == source) {
        buf[0] = size;
        buf[1] = 3;
        MPI_Ssend( buf, 2, MPI_INT, dest, 10, comm );
    }
    if (rank == dest) {
        MPI_Irecv( buf, 2, MPI_INT, source, 10, comm, &req );
    }
    MPI_Barrier( comm );
    /* At this point, we know that the receive has at least started, because of the Ssend. Check the status on the request */
    if (rank == dest) {
        status.MPI_SOURCE = -1;
        status.MPI_TAG = -1;
        MPI_Request_get_status( req, &flag, &status );
        if (flag) {
            if (status.MPI_TAG != 10) {
                errs++;
                fprintf( stderr, "Tag value %d should be 10\n", status.MPI_TAG );fflush(stderr);
            }
            if (status.MPI_SOURCE != source) {
                errs++;
                fprintf( stderr, "Source value %d should be %d\n", status.MPI_SOURCE, source );fflush(stderr);
            }
            MPI_Get_count( &status, MPI_INT, &count );
            if (count != 2) {
                errs++;
                fprintf( stderr, "Count value %d should be 2\n", count );fflush(stderr);
            }
        }
        else {
            errs++;
            fprintf( stderr, "Unexpected flag value from get_status\n" );fflush(stderr);
        }
        /* Now, complete the request */
        MPI_Wait( &req, &status2 );
        /* Check that the status is correct */
        if (status2.MPI_TAG != 10) {
            errs++;
            fprintf( stderr, "(wait)Tag value %d should be 10\n", status2.MPI_TAG );fflush(stderr);
        }
        if (status2.MPI_SOURCE != source) {
            errs++;
            fprintf( stderr, "(wait)Source value %d should be %d\n", status2.MPI_SOURCE, source );fflush(stderr);
        }
        MPI_Get_count( &status2, MPI_INT, &count );
        if (count != 2) {
            errs++;
            fprintf( stderr, "(wait)Count value %d should be 2\n", count );fflush(stderr);
        }
    }

    MPI_Finalize();
    return errs;
}

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